The rapid identification of microorganisms and other pathogenic antigens with the help of fluoroescent antibodies is a most important example of the diagnostic utility of fluorophoric protein conjugates. Existing procedures for fluorescent labeling of proteins, for example, labeling with fluorescin isothiocyanate (FITC) rely upon fluorophors with reactive functionalities which will covalently bind to proteins. However, this methodology is encumbered by serious disadvantages, stemming mainly from the need for extensive purification to remove any excess reagent which would otherwise non-specifically interfere in immunoassays.
It would thus be desirable to have a material for labeling which itself is non-fluorescent but which reacts with the materials to be labeled to produce fluorescent conjugates thus avoiding tedious purification.